Gmail is a free, advertising-supported email service offered as part of Google's G Suite, with 15GB of storage, color-coded inbox filters and unsend button.
Mandrill is a scalable and affordable email infrastructure service, with all the marketing friendly analytics tools they come to expect from MailChimp.
Mailchimp Transactional Email (formerly Mandrill) is a reliable, scalable and secure delivery API for transactional emails from websites and applications.